This paper shows the outcomes of a research carried out in a secondary school. The research investigates issues related to self-esteem in High School students. After defining the concept of self-esteem and revising other researches on the subject matter, we show how we have studied the relationship between self-esteem, personal variables and school performance. The study comes to the conclusion that self-esteem has an influence on academic and personal development during adolescence, being the degree of influence different depending on the type of self-esteem.